1. Field of the Invention
The present invention relates to a material testing method for evaluating mechanical properties of objects to be measured.
2. Description of Related Art
This type of material testing method is designed to determine the magnitude of a force acting on an object to be measured and the amount of strain on the object to be measured so as to evaluate mechanical properties such as an elastic coefficient of the object to be measured based on the measured force and strain. In the conventional method, the force acting on the object to be measured is measured with a force sensor such as a load cell (for example, see JSME Mechanical Engineers' Handbook, B3, p 74, published by The Japan Society of Mechanical Engineers (JSME) on Apr. 15, 1987).
A calibration technique (static calibration method) for the detection output of a force sensor system for detecting static forces is already established. However, when a dynamic force is exerted on the force sensor, unique phenomena occur, such as a delay in the response of the output of the sensor and the change in the shape of the output of the sensor. In use of the force sensor, the dynamic response must be determined in terms of the whole sensing system, such as a force sensing system consisted of a force sensor, an amplifier and a digital multi-meter. In this case, even when the detection output of the force sensor system is calibrated by the static calibration method, the dynamic force cannot be measured accurately. Thus, when a force acting on an object to be measured changes, the accuracy of measurement cannot be guaranteed even if the force is measured with the force sensor, and this makes it difficult to evaluate the mechanical properties of the object to be measured accurately. Furthermore, it is usually difficult to synchronize the measurement of force using a force sensor and measurement of strain using a displacement sensor, because both the force sensor and the displacement sensor have some delay in their output and the deformation of the shape of output signal.